build: Release SDK v5.9.1 (#2648)

Co-authored-by: github-actions[bot] <noreply@onesignal.com>

Author: github-actions[bot]

OneSignalSDK/gradle.properties

@@ -39,4 +39,4 @@ android.useAndroidX = true
 
 # This is the name of the SDK to use when building your project.
 # This will be fed from the GitHub Actions workflow.
-SDK_VERSION=5.9.0
+SDK_VERSION=5.9.1